Problem: Solve for $x$ : $x^2 + 7x - 18 = 0$
The coefficient on the $x$ term is $7$ and the constant term is $-18$ , so we need to find two numbers that add up to $7$ and multiply to $-18$ The two numbers $9$ and $-2$ satisfy both conditions: $ {9} + {-2} = {7} $ $ {9} \times {-2} = {-18} $ $(x + {9}) (x {-2}) = 0$ Since the following equation is true we know that one or both quantities must equal zero. $(x + 9) (x -2) = 0$ $x + 9 = 0$ or $x - 2 = 0$ Thus, $x = -9$ and $x = 2$ are the solutions.